1. Field of the Invention
The present invention relates to a glass yarn having a filament diameter of 3 to 9.mu., and more particularly to a glass yarn wound into a form of a square-end cheese package and a method of and an apparatus for manufacturing the same.
2. Description of the Prior Art
As well known, glass fiber is formed into hundreds of filaments by drawing, at high speed, molten glass flowed out through hundreds of orifices formed in the bottom of a bushing. Then, sizing agent is applied to the filaments followed by gathering the filaments into one strand. The strand is wound by a winding apparatus while traversing the strand by a traversing device, so that the strand is temporarily formed into a cake (see FIGS. 3A and 3B). At the time of use, the glass fiber is unwound from the cake to be used in either of two methods categorized as follows: the first method is a method in which a winding tube is removed after the cake has been heated and dried for a predetermined time, and the strand is drawn out from the inside of the cake (generally aforesaid method is called an "inside drawing method). Then, a predetermined number (usually 10 to 30) of the strands are paralleled to be wound up by a winder so that a glass roving is formed. As an alternative to this, the strands are supplied to a cutter to be formed into chopped strands which will be used as reinforcing materials for FRP or FRTP. In another method, the cake is dried naturally for a predetermined time, and the cake is set on a rewinder. The strand is drawn out from the outer portion of the cake while rotating the cake (in general the aforesaid method is called an "outside drawing method) so as to be twisted. As a result, a glass yarn is formed and the glass yarn is wound around a bobbin so as to be used in glass fiber texture.
The cake is formed into a barrel-like shape, the central portion of which projects outwardly as shown in FIG. 3A, because the strand is wound as described above while being traversed with an amplitude as shown in FIG. 3A in such a manner that the traversing device is also reciprocated within a stroke b. However, the degree of the projection over the central portion of the cake undesirably increases in proportion to the quantity of the wound strand. If the central portion of the cake projects excessively, the speed of the strand is always changed when the strand is wound while being traversed because the peripheral speed varies depending upon the position in the cake. The aforesaid speed change causes the speed of drawing the molten glass at the high speed to be changed. It leads to a fact that the size of the strand is undesirably changed. Therefore, a glass yarn composed of strands exhibiting an equal yarn count cannot be manufactured. If the degree of the projection is enlarged for the purpose of enlarging the quantity of the cake formed by winding the strands, the size of the strand cannot be included in a predetermined range. Therefore, the strand cannot be wound to form the projection of the cake that is larger than a certain degree. As a result, the inner diameter of the cake tends to be enlarged in order to enlarge the quantity of the cake formed by winding the strand, resulting in an excessively large size of the cake. Furthermore, the aforesaid large cake is formed into a thin shape. What is worse, the two terminative ends of the cake are formed into excessively thin and sharpened shape. Therefore, the cake cannot easily be handled. It is very difficult for a user to handle the cake as it is, and the cake cannot easily be packaged up for transportation. Even if the cake can be packaged up, the size of the package becomes too large with respect to the quantity which can be transported, causing a problem of unsatisfactory transportation efficiency. As a result, there arises an economical problem in terms of practical use if the strand wound into the cake is made to be a product as it is. Therefore, the aforesaid post-process must be performed.
In the case of the glass yarn, the strand is rewound from the cake to be formed into a yarn package while being twisted to be a predetermined degree as described above. A rewinding twister to be used in the aforesaid process has a creel on which a cake having a winding tube can be mounted. The strand is drawn out from the outer portion of the cake mounted on the delivery creel followed by twisting the strand by an ordinary twisting mechanism. Then, the strand is wound to be formed into the yarn package.
Methods of delivering the strand from the creel are categorized into a method in which the creel is drivingly rotated, and a method in which the rotation of the creel is made free to draw out the strand at a predetermined speed. It is considered to employ the rotation driving method to deliver the strand in order to prevent generation of fluff. If the thickness of the cake formed by winding the strand is large, the number of twist in the inner layer and that in the outer layer are therefore different from each other. As a result, a problem arises in a post-process such as the doubling and twisting process and the weaving process. The aforesaid fact has been one of the reasons that the thickness of the cake for the glass yarn cannot be enlarged considerably.
Furthermore, the glass yarn is different from the glass roving in a necessity of having a satisfactory constant-length rate. Since glass yarns shorter than a predetermined length or glass yarns that have adhesive portion cause the yield in the following process or the quality of the product to deteriorate, such glass yarns cannot be used freely. Since the roving is used in the form of glass roving manufactured by paralleling 10 to 30 strands or in the form of chopped strands obtained by cutting the strand to have a predetermined length, the constant-length rate is not the critical factor.
The constant-length rate of the glass yarn depends upon the cut ratio during the time of the spinning process and the cut ratio during the time of the rewinding process. The cut ratio per cake rises in proportion to the length of the glass yarn wound to form the cake. On the other hand, the constant-length rate is lowered in inverse proportion to the length of the wound glass yarn. Hence, the quantity of the wound glass yarn is ordinarily made to be 8 kg in the case of ECG75 (400 filaments of 9.mu. having a tex count of 67.5) and 3.5 kg (200 filaments of 7.mu. having a tex count of 22.5).
Tension (per tex count) acting on the strand at the time of the spinning process increases in inverse proportion to the diameter of the filament if the residual conditions for the glass fiber are the same. Therefore, the glass yarn is applied with a large spinning tension per tex because the glass yarn has a smaller filament diameter than the roving. The enlargement of the spinning tension for the glass yarn is in inverse proportion to the diameter of the filament. If the quantity of winding to form the cake is enlarged, the large spinning tension causes a problem of the quality of the thread in the inner layer to arise because the pressure of winding acting on the inner layer of the cake is enlarged. That is, the thread in the inner layer easily encounters cracks and easily generates fluff. For example, a glass yarn having a filament diameter of 3.mu. and known as a beta-yarn cannot be substantially used due to deterioration of the threads in the inner layer thereof if the quantity of the cake is made to be 2 kg or more. Because of the aforesaid reasons, it has been considered that the quantity of the wound glass yarn is limited to about 150,000 m under excellent conditions although it depends upon the filament diameter and the number of filaments.
The glass yarn has been used in a variety of ways and therefore the glass yarn must meet various requirements. For example, there arise a desire for a non-twisted glass yarn recently although the glass yarn has been considered to have a predetermined twist.
In the glass yarn wound to form the cake shape, the strand wound at a terminative end portion of the cake and the strand wound at the central portion are different from each other in the yarn count. Therefore, the yarn count varies in one strand in accordance with the period of the traverse. The aforesaid phenomenon becomes excessively in proportion to the quantity of the cake. Although it is preferable that the quantity of the wound glass yarn be large in terms of the control in the following process, the quantity of winding is limited because the dispersion of the yarn counts must be prevented.
Since the cake is formed into a shape having two thin ends pointed as shown in FIG. 3A, it cannot easily be handled. If the end portion is damaged, the strand can be cut at the damaged portion when the strand is drawn out from the cake. Therefore, it is very difficult to transport and package the cake.
Recently, there has been a desire for a non-twisted glass yarn. Although the barrel-like shape is very suitable to winding the strand to form the cake and rewinding the same by the rewinding twister while twisting it, it is not suitable to rewind the strand while omitting twisting.
If the strand is wound up while placing the cake stationarily in such a manner that substantially no twist is given, for example if the strand is intended to be drawn out from the inside of the cake placed horizontally, an adjacent strand is undesirably drawn out together with the desired strand. That is, a so-called scramble drawing phenomenon takes place and therefore the strand cannot be drawn out as desired. The reason for this is that a wire traverse method for traversing the cake for the glass yarn cannot accurately control the traversing angle. Another reason is that the employed starch type sizing agent, which is dried by air, cannot retain the shape of the cake. Therefore, the strand can easily be separated from other strands if a small impact is applied.
If the strand is intended to be drawn out from the cake placed vertically, the lower end portion is undesirably bent and deformed by the weight of-the cake because the end portion of the cake is thinned and pointed. As a result, the strand which is being drawn out can be caught and cut at this position. If the cake including the winding tube is placed vertically, the strand which is being drawn out comes in contact with and rubs the central portion in which the strands are wound densely in the case where the strand is drawn out from the lower portion of the cake because the central portion of the cake has a large thickness and the thickness decreases toward the two ends. As a result, fluff easily takes place, causing the strand to finally be cut. As described above, it is difficult to obtain non-twisted glass yarn from the glass yarn wound to form the cake shape. What is worst, the conventional glass yarn has a limitation in the quantity of winding and the length of winding. Therefore, there arises a problem that a requirement to enlarge the quantity of winding made from the following process cannot be met. The enlargement of the quantity of winding has been become important because the glass yarn has been used widely as well as the conventional requirement made by the following glass yarn process.